JPH05186992A - Method and equipment constitution for processing black liquor - Google Patents

Abstract

PURPOSE: To provide a method and apparatus constitution for recovering chemicals and heat contained in black liquor in a sulfate pulp process. CONSTITUTION: The black liquor is concentrated in an evaporation plant including a pressure heating reactor, after which the black liquor is gasified or combusted in a reactor (10) to produce hot gases. The hot gases formed in the reactor (10) are introduced into gas turbine power plant (16). The exhaust gases from the gas turbine (40) are introduced into a waste heat bioler, where steam is generated for a steam turbine power plant. Secondary steam is led from the pressure heating reactor as injection steam into the gas turbine.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a method and apparatus for treating black liquor of a sulfate pulp process to recover chemicals and heat therefrom. The method involves gasifying and / or burning black liquor in a pressurized gasifier or combustion reactor. Molten salts and / or solid salts produced during gasification and / or combustion are introduced into a dissolution tank for recovery of cooking chemicals,
The gas generated during this process is sent to a gas turbine through a refining process to recover energy from the gas.
From the gas turbine, exhaust gas is sent to the waste heat boiler,
The remaining energy is recovered as high pressure steam for use in steam turbine power plants.

[0002]

BACKGROUND OF THE INVENTION Recovery of cooking chemicals and heat is an essential step in the production of sulfate pulp. In modern pulp mills, the recovery process is usually done by burning black liquor in a boiler. The drug substance is
The organic matter recovered in the soda melt and dissolved from the wood burns, generating heat, which is recovered from the heat transfer surfaces arranged in the boiler. It has also been proposed to recover the chemical drug substance by gasifying the black liquor. In this case, in addition to the molten chemical agent substance, a gas with a high heat value is generated in the gasifier, which gas can be used, for example, in a gas turbine.

The black liquor obtained from the pulp-washing step after digestion has a dry solids content of only about 15-20%. Therefore, it is not possible to introduce it into the recovery boiler or the gasification furnace as it is to burn or gasify it.

The evaporation plant in a pulp mill is
It concentrates the black liquor to the extent that the dry solids can be combusted or gasified sufficiently. The maximum energy recovery from black liquor is to concentrate to the maximum dry solids content. With current technology, this is about 65-80%
Is.

The heat power required for evaporation comes from the steam or hot fumes produced during the process. Today, evaporation is usually done in heat exchangers using steam from a recovery boiler.

Increasing the dry solids content increases the heat consumption of the evaporation plant. This is because the amount of water to be evaporated increases. However, this is more valuable as the increased heat production of the combustion process is much greater than the additional heat required for evaporation. The additional heat thus generated in the recovery boiler can be recovered as high-pressure steam.

Previously, some recovery boiler configurations have involved the final concentration of liquid in a flue gas direct or cyclone evaporator. The reason for doing this is that concentrating in the heat exchanger to a dry solids content of> 50% has proven difficult because the heat transfer surface is very dirty. However, direct flue gas evaporators have some drawbacks, for example: -the presence of odors and emissions from the evaporator, -the reduced conversion efficiency of steam generation in the boiler, -evaporation in one step only. Therefore, it is not possible to use the secondary steam discharged from the evaporator.

Due to the drawbacks mentioned above, a recovery boiler fitted with a flue gas direct contact evaporator installation will, in later years, perform the final cooling of the flue gas with a water preheater and a separate final concentration of the liquor. It was modified to work with the attached evaporator.

The above-mentioned drawbacks are due to the fact that the Finnish patent application No. 8
This can be partially avoided by using a final concentration device for the liquid as suggested in US Pat. No. 54,549. In this device, the effluent is heated using the fumes produced by pressurized combustion and the heat capacity of the fumes after the boiler by indirect heat exchange. Heating by flue gas is performed at a concentration such that the liquid does not adhere to the heat transfer surface. The heated and pressurized liquid is then expanded to a low pressure, thus evaporating the water from the liquid and concentrating the liquid. This enrichment is carried out in another means which does not have a heat transfer surface which risks fouling. The implication of this specification is that the secondary steam thus generated can replace the primary steam of an evaporation plant connected in series. In this way, the liquid is heated from 80 to 120 ° C to 16 ° C.
It can be heated to 0-250 ° C. and concentrated to a dry solids content of> 55%. However, sulfur emissions from recovery boilers and evaporation plants are unavoidable.

Sulphate pulp mill mill sulfur emissions originate primarily from recovery boilers, evaporation plants and cooking plants. To date, in the case of black liquor, the higher the dry solids content achieved by evaporation, the lower the sulfur emissions of the flue gas from the recovery boiler. Conversely, the sulfur content of green liquor increases with increasing dry solids content, and therefore the sulfur content of both white and black liquor also increases. There is also reason to believe that evaporation plant sulfur emissions are increased when the black liquor has a high sulfur content.

As energy prices continue to increase, it becomes increasingly important to obtain high conversion efficiency of electricity generation during chemical recovery. Combustion heat generated during black liquor combustion in a recovery boiler must be mainly recovered as steam. To avoid boiler corrosion,
This means that maximum conversion efficiency cannot be obtained during power generation, since the steam P and T values must be relatively low. The high pressure steam generated is introduced into a back pressure steam turbine and the steam from the discharge side is used to meet the heat demand of the pulp mill. A turbine and a generator attached to it generate electricity necessary for a pulp mill. However, the conversion efficiency of power generation is only about 20-25%. Although the recovery boiler has become a reliable regeneration and energy generation process, the heat / power ratio obtained here is a disadvantage to the current sulfate pulp mill. Today, heat generation in recovery boilers fits very well with the current demand, but the conversion efficiency of generated power is poor.

In pulp production, steam consumption can no longer be expected, while electricity consumption is especially high.
Paper-integrated manufacturing plants still tend to increase.

Given the circumstances described above, the reason why long-term research has been continued on how traditional recovery boilers can be replaced with new processes, such as black liquor gasifiers. Has become. Many alternatives are currently being researched. Common to the proposed new process is the separation of drug regeneration and energy production and the delivery of the produced fuel to combined power plants.

Black liquor can be gasified in many ways. Reputable methods currently under consideration are, for example, solid phase gasification and melt phase gasification. The gas generated from gasification can be combusted in either a conventional boiler or a combined pressure process to generate steam and electricity.

[0015] Finnish patent application No. 841540 suggests the pressurized gasification of black liquor, which would give the opportunity to apply combined power generation techniques in the production of electricity in pulp mills. According to this method, combustible gas is produced by gasification, and the sulfur content of black liquor is converted to sulfide to a considerable extent. Black liquor (concentration 45 ~
75%) is introduced into the gasifier as an aqueous solution. The gas produced in the gasification is purified and burned into hot flue gas, which is then used in a gas turbine for power generation. The exhaust gas from the gas turbine is fed to a waste heat boiler, where the heat of the exhaust gas is used here to generate steam for a steam turbine plant. In addition to electricity, this steam turbine system also produces process steam.

The black liquor aqueous solution is supplied as fine droplets to the upper part of the gasification furnace. Prior to gasification, the black liquor droplets dry in a hot gas stream rising from the bottom of the gasifier. The solid content or the molten salt residue content of the gasified black liquor accumulates in the lower part of the gasification furnace and is further introduced into the melting tank to recover the cooking chemicals. The water evaporated from the black liquor exits the gasification furnace from the upper part of the gasification furnace together with other vaporized components together with the produced gas.

Therefore, the gas from this gasification furnace contains both the gas produced by the gasification of the black liquor and the water and / or the vaporizable alkali and the sulfur compound evaporated from the black liquor being concentrated. Become. It is necessary to separate harmful substances from the gas prior to introducing the gas to the gas turbine. Thus, the gas is, for example, led to an absorption column where the sulfur compounds are removed from the gas and then to, for example, a wet scrubber for final purification.

The drawback of the black liquor gasification system suggested above is that the gas contains a large amount of water vapor. The more steam the gas contains, the poorer its combustion characteristics and the lower the conversion efficiency of power generation in the gas turbine.
In addition, a large-scale gas purification system is required due to the large amount of exhaust produced in this way, and at the same time, the gas produced by evaporation to remove harmful substances from the gas prior to introducing it to the gas turbine. Also, it is necessary to purify the gas generated by the gasification together. The cost of purifying this gas will be substantial.

The conversion efficiency of power generation in a gas turbine is also
It is usually reduced by the relatively large amount of air required by the gas turbine to reduce the inlet temperature. In other words, this large amount of dilution air increases the required power of the compressor and thus reduces the conversion efficiency of power generation in the gas turbine.

It is an object of the present invention to provide an improved method of recovering chemicals and heat from black liquor and to minimize the above mentioned drawbacks of prior art recovery methods.

[0021] A main object of the present invention is to provide a method and apparatus for recovering chemicals and heat quantity from black liquor, which has the maximum conversion efficiency of power generation.

Another object of the present invention is to provide an improved temperature control method for a gas turbine in a black liquor heat recovery plant.

Yet another object of the present invention is to provide a method for minimizing the harmful emissions caused by the final evaporation of black liquor.

[0024]

The method of the present invention for recovering chemicals and heat from black liquor in a sulfate pulp manufacturing process, ie, the black liquor is gasified (and / or burned) and the gas is used for power generation. The main advantage of the gas turbine expanded method is that the pressurized secondary steam from the sulphate pulp manufacturing process is fed to the gas turbine combustor before the gas turbine blades to control the gas turbine inlet temperature. Is introduced into the combustion gas therein as injection steam. This secondary steam produced in the sulfate pulp manufacturing process can be used, for example, for temperature control, but is not limited to, for example, a cooking plant, an expansion step,
Secondary steam from a drying process or evaporation plant. This secondary steam can be further pressurized to the pressure level of the gas turbine.

The device according to the invention therefore comprises the following equipment: a black liquor evaporator for concentrating the black liquor, a pressurized reactor for gasifying or burning the black liquor concentrated in the evaporator, an addition Gas refining means for refining the gas generated in the pressure reactor, -Gas turbine power plant for recovering energy from the purified gas, -Waste heat boiler for recovering heat as pressurized steam from turbine exhaust, and-Waste heat boiler It includes a steam turbine power plant that recovers energy from the generated steam and features a pressure-heated reactor that acts as an evaporator for black liquor, which is connected by a conduit to a gas turbine or gas turbine combustor. The pressurized secondary steam from the pressure heating reactor is introduced into the gas turbine as injection steam from this conduit.

Since a significant amount of secondary steam is generated prior to gasification (or combustion), especially in connection with vaporization plants and pressure heating of black liquor, the present invention provides that the black liquor precedes gasification or combustion. A description will be given below with reference to an arrangement in which the secondary steam which is pressure-heated and generated in the pressure-heating step is introduced into the gas turbine in order to reduce its inlet temperature.

According to a preferred embodiment of the invention, the black liquor is evaporated by conventional evaporation and pressure heating methods to a high content of dry solids, which is an overall advantage. After that, the black liquor is gasified and the energy content of the gas obtained by gasification is recovered in a combined gas turbine / steam turbine power plant. The secondary steam generated by pressure heating, which contains water and other evaporative components, is introduced into the gas turbine combustor and controls the temperature of the combustion gas generated there, prior to guiding the combustion gas to the turbine blades. To a suitable temperature. The steam needed to pressure heat the black liquor is received from the steam turbine.

The method of the present invention provides an advantageous method of recovering secondary steam discharged from the pressure heating step. This is done by injecting the steam into the gas turbine as injection steam. Supplying the secondary steam to the gas turbine requires less excess air volume, which is normally required to control the temperature of the gas entering the blades of the gas turbine. This reduces the power requirements of the compressor and makes this process more effective.

In the process where the black liquor is burned rather than gasified, the secondary steam from pressure heating and the flue gas from the combustion can be combined before being introduced into the gas turbine. In this way, the volume that flows through the gas turbine is increased and thus the amount of power generation is also increased in this black liquor combustion process. Combining this secondary steam with the flue gas will result in a system that advantageously purifies the secondary steam in the combined secondary steam and flue gas scrubber.

The pressure heating process, that is, the heat treatment of the liquid, can be carried out in the middle of evaporation or immediately before gasification or combustion. In the pressure heating, the temperature of the black liquor is higher than the cooking temperature, preferably 170 to 200 ° C., in order to decompose the huge lignin portion contained in the black liquor.
Raise to. Compounds containing sulfur or alkali are
It is easily evaporated from black liquor in the pressure heating process.
The most economical heating system can be selected, however, for example, direct or indirect heating with steam, other heating systems such as electric heating are also selected. Reheated steam from a steam turbine power plant is preferably used as the heat source for pressure heating. The viscosity of black liquor can also be reduced by pressure heating, which in addition to improving black liquor processing properties and evaporative properties, also helps transfer black liquor from one process to another. become. Therefore, pressure heating can concentrate the black liquor to the maximum dry solids content, thus effectively increasing the combustion value of the black liquor, resulting in a combined gas turbine /
The conversion efficiency of power generation in the steam turbine power plant is also increased. As the dry solids content of black liquor increases, the effective gas flow from the gasifier or recovery boiler increases. Therefore, the amount of electricity generated by the gas turbine increases, the amount of steam generated by the waste heat boiler also increases, and as a result, the amount of power generated by the steam turbine also increases.

In the combined power plant, it is possible to convert excess secondary steam generated by pressure heating into electric power by injecting it into the gas turbine as injection steam. The pressure of this secondary steam must be high enough to successfully supply pressurized gas. Steam injection also increases the conversion efficiency of power generation and gas turbine efficiency, and reduces the need for excess air that must be introduced into the gas turbine by the compressor. For a gas turbine with an excess air level of about 1.4, steam injection would give about 1.15.
Can be reduced to.

The change in volume of air that must be compressed by the compressor is an important factor for the process. Injecting secondary steam into the combustion gas entering the gas turbine according to the invention also reduces the temperature of the combustion gas, so that the temperature of the gas entering the blades of the steam turbine can be kept constant by steam injection. Therefore, the amount of cooling excess air compressed by the compressor can be reduced in proportion to the amount of injected steam. In some gas turbines, the compressor is equipped with a set of adjustable guide vanes. The output of the compressor can be adjusted by such vanes. The economical adjustment range is rather narrow, 80 to 100%. The gas turbine can be operated in other regulation ranges as well, but in this case the compressed gas temperature will probably decrease with increasing steam injection.

The secondary steam introduced into the gas turbine needs to be cleaned before it can be introduced into the turbine.
The secondary steam resulting from pressure heating also contains, for example, sulfur compounds, alkaline compounds, and possibly other harmful substances, which must be removed from the secondary steam before it is introduced into the gas turbine. The gas from the gasification process also needs to be purified. The gas streams are purified separately, which means that it is possible to use the most suitable purification method separately for different harmful compounds of secondary steam and gas. However, it is also possible to combine the gas purification process so that both systems use, for example, the same absorbent. Although the actual purification is carried out on different equipment, the absorption liquid can be regenerated on one and the same equipment, which is cheaper.
If the secondary steam is purified in a separate device, a small amount of secondary steam can be efficiently produced by a relatively simple means. Sulfur compounds can be removed more easily from small amounts of secondary steam than from large steam and gas merges. Furthermore,
It is advantageous to remove the sulfur compounds from the secondary steam before they contact the air in the gas turbine compressor. The pressurized secondary steam flow is relatively small,
Therefore, the plant required for this refining can be small. The advantage for the overall process is to purify the gas at the highest possible temperature so that the thermal energy contained in the gas can be used in the gas turbine.

Pressure heating is the same pressure as gasification or combustion,
For example, it can be carried out at about 20 bar. However, based on the value of steam used for heat treatment,
The heat treatment may be performed at a pressure higher or lower than the pressure of the gasification furnace. Prior to introducing this gas into the gas turbine combustor, the pressure of the secondary steam from the heat treatment needs to be adjusted by a pressure relief valve or by increasing the pressure.

The pressure heating of black liquor and the use of secondary steam as injection steam according to the invention are particularly suitable for the gasification of black liquor. This is because if the dry solid content of the black liquor is high, it has an extremely advantageous effect on the gasification of the liquor. Therefore, lowering the viscosity of the liquid by pressure heating means
It makes a great contribution to the gasification process.

Gasification of black liquor with a high dry solids content produces a gas with a high thermal value, which can be efficiently used in a combined gas turbine / steam turbine power plant. The gasification is preferably carried out at an elevated temperature, so that the inorganic substances in the black liquor are expelled from the reactor in the molten state and the molten one can be further processed in a convenient manner.

The invention is further described below by way of example with reference to the accompanying drawings, in which: The accompanying drawings are schematic views of the pressure heating system of the present invention, which constitutes a black liquor gasification plant.

The illustrated gasification plant includes a black liquor gasification reactor 10, a pressure heating means 12, a gas refining means 14, a gas turbine power plant 16 and a steam turbine power plant 18.

The black liquor is supplied to the pressure heating reactor 12 by the pump 22. In the pressure-heated reactor, it is indirectly heated by directing the reheated steam from the steam power plant by conduit 24 to the heat exchanger 26. The black liquor is heated to a temperature of 180 to 200 ° C., for example. The pressure is about 10-20 bar in the pressure-heated reactor.

The concentrated black liquor is led from the pressure heating step to the final evaporation step 28 by conduit 27 and by conduit 29 to the gasification furnace 10. The water evaporated from the black liquor is introduced into the steam refining means 15 via the conduit 30 together with other easily gasified components. Here, it is preferred that sulfur and other substances harmful to the gas turbine plant, such as alkaline compounds, be removed from this secondary steam.

The gas produced in the actual gasification furnace 10 is led to the gas refining plant 17 via the conduit 11, where it is cleaned separately from the secondary steam coming from the pressure heating process. The melt generated in the gasification furnace is discharged through the chute 13.

The refined steam and refined gas streams from the gas refinery are both withdrawn via conduits 32 and 34 and withdrawn to a gas turbine combustor 36 to produce hot combustion gases. The secondary steam flow from conduit 32 cools the combustion gases generated in the combustor. Combustion gas and secondary steam therewith are conducted from the combustor to a gas turbine 40 via conduit 38. The generator 42 for power generation and the compressor 44 for producing compressed air are mounted on the same shaft as the gas turbine. Compressed air is conducted from the compressor to the gasifier 10 via conduit 46 and to combustor 36 via conduit 48.

Exhaust gas from the gas turbine is led to a waste heat boiler 52 via a conduit 50 and the remaining heat of the gas is used for steam generation. The cooled gas is led from the waste heat boiler to the chimney via conduit 54.

In the steam turbine system 18, the feed water is led from the feed water tank 56 through the conduit 58 to the steam generator 60 arranged in the waste heat boiler. The high-pressure steam generated by the steam generator is guided to the steam turbine 64 via the conduit 62. The generator 66 for power generation is mounted on the same shaft as the steam turbine. The reheated steam is removed from the steam turbine and directed to the pressure heater 12 via conduit 24. The low pressure steam, and possibly also the reheated steam, is delivered via conduits 68 and 70 to the means 7
Sent to 2. From this means the condensate is recycled to the water supply tank 56 via conduit 74. The water condensed from the steam from the heat exchanger 26 is also returned to the water tank through the conduit 76.

The gasifier pressure is preferably equal to the pressure heating plant pressure. However, in the embodiment of the accompanying drawings, the pressure of the gasification furnace is higher than the pressure of the pressure heating plant, so that the pressure raising means 78 is used.
It is placed after 2 to increase the pressure of the secondary steam to the level of the pressure of the gas coming from the gasifier.

The above device configuration is merely an embodiment of the present invention, and the details of the present invention may differ from the above configuration and may be modified within the scope of the invention described in the claims. obtain.

[Brief description of drawings]

FIG. 1 is a schematic view of a pressure heating system of the present invention, which constitutes a black liquor gasification plant.

[Explanation of symbols]

10 ... Black liquor gasification reactor, 12, ... Pressure heating means, 1
4 ... Gas refining means, 16 ... Gas turbine power plant, 18 ... Steam turbine power plant, 36 ... Gas turbine combustor, 40 ... Gas turbine, 52 ... Waste heat boiler, 78 ... Pressure raising means

[Procedure amendment]

[Submission date] February 5, 1992

[Procedure Amendment 1]

[Document name to be amended] Statement

[Name of item to be amended] Claims

[Correction method] Change

[Correction content]

[Claims]

Claims (16)

[Claims] 1. A method of treating black liquor in a sulphate pulp making process to recover chemicals and heat from the black liquor, ie evaporating the black liquor to increase its dry solids content, an evaporator. The black liquor from the above is gasified and / or burned in a pressure reactor to produce a high temperature gas, and the molten salt and / or solid salt produced in the reactor is introduced into a dissolution tank to recover a cooking chemical. -Refining the gas produced in the reactor, -introducing the purified gas into a gas turbine to recover energy of the gas, -introducing exhaust gas from the gas turbine into a waste heat boiler to generate steam. In a method for generating and recovering energy from steam generated in a steam turbine power plant, pressurized secondary steam from a sulphate pulp manufacturing process is used to control the gas turbine inlet temperature. Of the black liquor in the sulphate pulp manufacturing process, characterized in that it is introduced into the combustion gas therein as injection steam to the gas turbine combustor before the blades of the gas turbine. How to recover from. 2. A method of treating black liquor to recover chemicals and heat from the black liquor, comprising: -heating the black liquor by heat exchange contact with high temperature steam prior to gasification and / or combustion to achieve overall 2. A process according to claim 1, characterized in that the black liquor is concentrated to a very high dry solids content, and-the secondary steam discharged from the black liquor in pressure heating is introduced into the gas turbine as injection steam. 3. The method according to claim 1, wherein the pressure heating of the black liquor is carried out in indirect heat exchange contact with hot steam. 4. The method according to claim 1, wherein the pressure heating of the black liquor is carried out in direct heat exchange contact with hot steam. 5. The method of claim 1 wherein the black liquor pressure heated and concentrated to a high dry solids content is gasified to produce a hot gas. 6. The method of claim 1 wherein the black liquor is pressure heated by reheat steam coming from a steam turbine power plant. 7. Before directing the secondary steam to the gas turbine,
The secondary steam is purified, and the secondary steam is purified.
The method described. 8. A process according to claim 7, characterized in that secondary steam is introduced into the absorption means in order to remove sulfur compounds from the secondary steam. 9. The method according to claim 7, wherein the secondary steam and the hot gas produced in the gasification or combustion are purified by separate absorption means, but with the same absorbent. 10. The method of claim 7 wherein the secondary steam is purified to remove alkaline compounds from the secondary steam. 11. Process according to claim 1, characterized in that a final evaporation of the black liquor is carried out after pressure heating, prior to gasification and / or combustion. 12. The method according to claim 2, wherein the pressure of the pressure heating is the same as the pressure of the gasifier or the combustion reactor. 13. The method according to claim 2, wherein the pressure heating is performed at a temperature of 180 to 200 ° C. 14. A device structure for recovering the chemicals and heat quantity of black liquor, that is, a black liquor evaporator (12, 28) for concentrating black liquor, and gasifying or burning the black liquor concentrated in the evaporator. Pressure reactor (10),-Gas refining means (17) for purifying gas generated in the pressure reactor, -Gas turbine power plant (16) for recovering energy from the purified gas, -Pressurized steam from turbine exhaust In a device configuration including a waste heat boiler (52) for recovering heat as heat and a steam turbine power plant (18) for recovering energy from steam generated in the waste heat boiler, pressure heating acting as an evaporator for black liquor A reactor (12) is included, the evaporator being connected to a gas turbine (40) or a gas turbine combustor (36) by conduits (30, 32) for pressure heating reaction. The equipment configuration is characterized in that the pressurized secondary steam from the reactor is introduced into the gas turbine as injection steam. 15. Steam refining means (15) is arranged between the pressure heating reactor and the gas turbine power plant to purify the secondary steam.
The device configuration according to 4. 16. A pressure raising means (78) is arranged between the pressure heating reactor (12) and the gas turbine power plant to raise the pressure of the secondary steam before introducing the secondary steam to the gas turbine power plant. 15. The device configuration according to claim 14, wherein: